ITU H.324 Recommendation, which is hereby incorporated by reference herein in its entirety, dictates the protocol that is used with 3G terminals in setting up media channels for media transmission. As part of this protocol, messages specified in ITU H.245 Recommendation, which is hereby incorporated by reference herein in its entirety, are exchanged between a local terminal and a remote terminal.
One problem with H.324 is that call set-up is a long process mainly due to a series of H.245 messages that are exchanged by two terminals. Today, to open a call with an audio and a video channel, usually ten or more H.245 messages need to be exchanged. This requires three to ten round trips of messages. Even more messages may be required to handle channel conflicts or overcome noisy communication lines.
Turning to FIG. 1, a simplified block diagram of two terminals communicating via a conventional network is shown. As illustrated, a local terminal 11 communicates with a remote terminal 12 via a network 13. Local terminal 11 and remote terminal 12 may be for example, devices for engaging in 3 G communications, and may be wired or wireless devices, such as 3G mobile telephones, servers, etc. Network 13 may be any kind of circuit switched network, or any other network that may be used to pass H.324 data. For example, network 13 may be a network supporting 3G connections such as an Integrated Services Digital Network (ISDN), a Public Switched Telephone Network (PSTN), a Transmission Control Protocol (TCP) network, and the like.
FIGS. 2A and 2B illustrate an example of how terminals 11 and 12 may set up a call using a conventional H.324 protocol. As shown, at step 21, an H.245 TerminalCapabilitySet request (TCS) message and an H.245 MasterSlaveDetermination request (MSD) message are sent from each terminal and received by the other. The TCS messages indicate the respective capabilities of terminals 11 and 12, such as supported audio and video codecs, supported features and services, supported adaptation layers, and so on. The MSD messages determine the master/slave relationship of terminals 11 and 12.
Subsequently, at step 22, each terminal acknowledges the other's TCS and MSD messages by sending an H.245 TerminalCapabilitySetAck response (TCS Ack) message and an H.245 MasterSlaveDeterminationAck response (MSD Ack) message. At this point, both terminals recognize the type of codecs they can use and which of terminals 11 and 12 is the master or the slave of this call.
Next, at step 23, H.245 OpenLogicalChannel request (OLC) messages are sent and received by terminals 11 and 12. Generally, a single video channel and a single audio channel are opened.
H.245 OpenLogicalChannelAck response (OLC Ack) messages, acknowledging the receipt of OLC messages, are then sent and received at step 24. Sometimes, H.245 OpenLogicalChannelReject response (OLC Reject) messages are sent, which might require additional messages to resolve the situation to be sent.
At step 25, H.245 MultiplexEntrySend request (MES) messages are sent and received by terminals 11 and 12 to enable an H.223 multiplexing (MUX) entry table to be exchanged. The H.223 MUX entry table allows terminals 11 and 12 to demultiplex the media sent on the opened channels.
Next, at step 26, H.245 MultiplexEntrySendAck response (MES Ack) messages are then sent and received by terminals 11 and 12 to acknowledge the MES message received from the other terminal.
Finally, after this entire exchange of messages, media is sent and received at step 27.
As can be seen, the conventional method requires that at least ten messages be handled by each terminal before media is sent or received. Such a large number of messages introduces a large delay to the call set-up process. Hence, a method for speeding up the call set-up process may be desirable and may offer many significant advantages over the currently utilized call set-up methods. The above illustrates the “best-case” scenario, where all goes well. In cases of problems, retransmissions or additional messages might be required.